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Abstract:

A hearing aid includes: first and second microphones; first and second
A/D converters; a microphone sensitivity correction unit; a hearing
assistance processing unit; a microphone sensitivity correction value
calculation unit; a storage unit; a failure detection unit; a sound
output unit; a D/A converter; and a receiver. The outputs of the first
and second A/D converters are input to the microphone sensitivity
correction value calculation unit. One output the microphone sensitivity
correction value calculation unit is connected to the microphone
sensitivity correction unit, and another output thereof is connected to
the storage unit. An output of the storage unit and a signal output from
the another output of the microphone sensitivity correction value
calculation unit are input to the failure detection unit. Output signals
of the failure detection unit and the hearing assistance processing unit
are input to the sound output unit.

Claims:

1. A hearing aid comprising: a first microphone; a first A/D converter
connected on an output side of the first microphone; a second microphone;
a second A/D converter connected on an output side of the second
microphone; a microphone sensitivity correction unit connected on an
output side of the second A/D converter; a hearing assistance processing
unit to which an output of the microphone sensitivity correction unit and
an output of the first A/D converter are input; a microphone sensitivity
correction value calculation unit to which the output of the first A/D
converter and an output of the second A/D converter are input, and one
output of which is connected to the microphone sensitivity correction
unit; a storage unit connected to another output of the microphone
sensitivity correction value calculation unit; a failure detection unit
to which an output of the storage unit and a signal output from the
another output of the microphone sensitivity correction value calculation
unit are input; a sound output unit to which an output signal of the
failure detection unit and an output signal of the hearing assistance
processing unit are input; a D/A converter connected on an output side of
the sound output unit; and a receiver connected on an output side of the
D/A converter.

2. The hearing aid according to claim 1, wherein the microphone
sensitivity correction value calculation unit comprises: a first digital
filter connected on an output side of the first A/D converter; a second
digital filter connected on the output side of the second A/D converter;
a correction unit connected on an output side of the second digital
filter; a comparison unit to which an output signal of the correction
unit and an output signal of the first digital filter are input; and a
correction value update unit connected on an output side of the
comparison unit.

3. The hearing aid according to claim 2, wherein the microphone
sensitivity correction value calculation unit comprises: a memory
connected on an output side of the correction value update unit; and a
selector to which an output signal of the memory and an output signal of
the correction value update unit are input, and which is configured to
select one of the signals.

4. The hearing aid according to claim 1, wherein the failure detection
unit comprises: an abnormal value setting unit connected on an output
side of the storage unit; an abnormal value detection unit to which an
output signal of the abnormal value setting unit and an output signal of
the microphone sensitivity correction value calculation unit are input;
and an abnormal time detection unit connected on an output side of the
abnormal value detection unit.

5. The hearing aid according to claim 1, wherein the sound output unit
comprises: an alarm sound generation unit connected on an output side of
the failure detection unit; and an output sound selection unit to which
an output signal of the alarm sound generation unit, the output signal of
the hearing assistance processing unit, and the output signal of the
failure detection unit are input, and which is configured to select one
of the output signal of the alarm sound generation unit and the output
signal of the hearing assistance processing unit and to output the
selected signal to the D/A converter.

6. The hearing aid according to claim 1, wherein the sound output unit
comprises: an alarm sound generation unit connected to the output side of
the failure detection unit; and an output sound synthesis unit to which
an output signal of the alarm sound generation unit, the output signal of
the hearing assistance processing unit, and the output signal of the
failure detection unit are input, and which is configured to combine the
output signal of the alarm sound generation unit with the output signal
of the hearing assistance processing unit and to output the synthesized
sound to the D/A converter.

7. The hearing aid according to claim 4, wherein the abnormal time
detection unit comprises: a first counter used for determining a failure
of the first microphone; and a second counter used for determining a
failure of the second microphone.

8. The hearing aid according to claim 7, wherein the sound output unit
changes a length of an alarm sound, which is to be output, based on
information of the first counter and the second counter.

9. The hearing aid according to claim 7, wherein the sound output unit
changes a type of an alarm sound, which is to be output, based on
information of the first counter and the second counter.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of International Application No.
PCT/JP2009/005933, filed on Nov. 6, 2009, which claims priority from
Japanese Patent Application No. 2009-025743 filed on Feb. 6, 2009, the
disclosures of which Applications are incorporated herein by reference.

BACKGROUND

[0002] 1. Technical Field

[0003] This invention relates to a technique of detecting a failure of a
microphone of a hearing aid.

[0004] 2. Description of Related Art

[0005] A hearing aid including two microphones for providing directivity
for the user includes a correction circuit described below configured to
eliminate an amplitude difference between output signals of the
microphones so as to correct difference in sensitivity caused by the
individual difference between the microphones (for example, see
JP-A-2003-506937).

[0006] The correction circuit includes: a first microphone; a first ND
converter connected on an output side of the first microphone; a second
microphone; a second A/D converter connected on an output side of the
second microphone; a microphone sensitivity correction unit connected on
an output side of the second A/D converter; a hearing assistance
processing unit to which an output of the microphone sensitivity
correction unit and an output of the first A/D converter are input; a
microphone sensitivity correction value calculation unit to which the
output of the first A/D converter and an output of the second A/D
converter are input, and one output of which is connected to the
microphone sensitivity correction unit; a D/A converter connected on an
output side of the hearing assistance processing unit; and a receiver
connected to an output side of the D/A converter.

SUMMARY

[0007] The related art described above can provide directivity by using
two microphones different in sensitivity. However, even when one
microphone fails and amplitude of an output signal of the microphone
lowers, the correction circuit operates so as to eliminate the output
signal amplitude difference between the two microphones. Thus, the user
can not recognize the failure of the microphone.

[0008] In view of the circumstances described above, an object of the
invention is to provide a hearing aid that can make the user recognize a
failure of a microphone.

[0009] In one aspect of the invention, a hearing aid includes: a first
microphone; a first A/D converter connected on an output side of the
first microphone; a second microphone; a second A/D converter connected
on an output side of the second microphone; a microphone sensitivity
correction unit connected on an output side of the second A/D converter;
a hearing assistance processing unit to which an output of the microphone
sensitivity correction unit and an output of the first A/D converter are
input; a microphone sensitivity correction value calculation unit to
which the output of the first A/D converter and an output of the second
A/D converter are input, and one output of which is connected to the
microphone sensitivity correction unit; a storage unit connected to
another output of the microphone sensitivity correction value calculation
unit; a failure detection unit to which an output of the storage unit and
a signal output from the another output of the microphone sensitivity
correction value calculation unit are input; a sound output unit to which
an output signal of the failure detection unit and an output signal of
the hearing assistance processing unit are input; a D/A converter
connected on an output side of the sound output unit; and a receiver
connected on an output side of the D/A converter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is an external view of a hearing aid according to an
embodiment of the invention;

[0011]FIG. 2 is a block diagram of the hearing aid according to the
embodiment of the invention;

[0016] FIGS. 7A to 7C are operation diagrams of the hearing aid according
to the embodiment of the invention; and

[0017]FIG. 8 is a block diagram to show another configuration of the
failure detection unit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0018] A hearing aid of the embodiment will be described below in detail
with reference to the drawings.

[0019] As shown in an external view of FIG. 1, a hearing aid of the
embodiment includes a face plate 1 and a shell 2 which are assembled. The
face plate 1 is provided with a microphone 3a (first microphone), a
microphone 3b (second microphone), a switch 4, a volume dial 5, and a
battery insertion port 6. The shell 2 is provided with a receiver 7 at a
position on the opposite side to the face plate 1.

[0020]FIG. 2 is an electrical diagram showing functional components
provided in the shell 2. The microphone 3a and the microphone 3b shown in
FIG. 1 are placed most upstream in the shell 2. In the shell 2, there is
provided: an A/D (Analog to Digital) converter 8a (first A/D converter)
connected on an output side of the microphone 3a; an A/D converter 8b
(second A/D converter) connected on an output side of the microphone 3b;
a microphone sensitivity correction unit 9 connected on an output side of
the A/D converter 8b; a hearing assistance processing unit 10 to which an
output of the microphone sensitivity correction unit 9 and an output of
the A/D converter 8a are input; a microphone sensitivity correction value
calculation unit 11 to which the output of the A/D converter 8a and an
output of the A/D converter 8b are input, and one output of which is
connected to the microphone sensitivity correction unit 9; a storage unit
12 connected to another output of the microphone sensitivity correction
value calculation unit 11; a failure detection unit 13 to which an output
of the storage unit 12 and a signal output from the another output of the
microphone sensitivity correction value calculation unit 11 are input; a
sound output unit 14 to which an output signal of the failure detection
unit 13 and an output signal of the hearing assistance processing unit 10
are input; a D/A (Digital to Analog) converter 15 connected on an output
side of the sound output unit 14; and the receiver 7 connected on an
output side of the D/A converter 15. In addition, there is further
provided: a control unit 16 configured to the microphone sensitivity
correction value calculation unit 11, the storage unit 12, and the
failure detection unit 13.

[0021] The microphone 3a and the microphone 3b are configured to collect
surrounding sound of the hearing aid, convert the sound into electric
signals, and output the signals to the A/D converter 8a and the A/D
converter 8b, respectively, as an analog input signal. The microphones
are placed on the face plate 1 at a given distance from each other as
shown in FIG. 1. Usually, the microphones are distant from each other
relatively front and rear such that one of the microphones is closer to
the front direction of the user (face side) and the other thereof is
closer to the back direction (head back side), and the microphones are
called front microphone and rear microphone.

[0022] In the embodiment, the case where the microphone 3a is the front
microphone and the microphone 3b is the rear microphone will be described
as an example. In the embodiment, the microphone sensitivity correction
unit 9 adjusts the amplitude of the output signal of the rear microphone
thereby performing a sensitivity correction. The signal of the front
microphone and the signal of the rear microphone which is subjected to
sensitivity correction are processed so as to provide directivity for the
user by a directivity control unit (not shown) provided in the hearing
assistance processing unit 10.

[0023] The A/D converter 8a and the A/D converter 8b are configured to:
sample analog input signals output by the microphone 3a and the
microphone 3b at the periods of an operation clock configured to drive a
digital circuit in the hearing aid; and output the signals as digital
input signals which represent the amplitude of the analog input signals
by multiple bits.

[0024] The microphone sensitivity correction unit 9 is configured to:
correct the amplitude value of the digital input signal output by the A/D
converter 8b by using the microphone sensitivity correction value output
by the microphone sensitivity correction value calculation unit 11; and
output the corrected amplitude value to the hearing assistance processing
unit 10 as a digital correction input signal. That is, the hearing aid
shown in the embodiment corrects the output signal of the microphone 3b
(rear microphone) so as to perform a sensitivity correction such that the
corrected signal has the same sensitivity as the output signal of the
microphone 3a (front microphone). The microphone sensitivity correction
value is a value to be multiplied by the digital input signal although
described later in detail. Therefore, the microphone sensitivity
correction unit 9 is implemented as a multiplier configured to multiply
the amplitude value of the digital input signal by the microphone
sensitivity correction value.

[0025] The digital input signal input from the A/D converter 8a and the
digital correction input signal input from the microphone sensitivity
correction unit 9 are input to the hearing assistance processing unit 10,
and the hearing assistance processing unit 10 performs hearing assistance
processing matched with the hearing characteristic of the user and
outputs the process signal to the sound output unit 14 as a digital
hearing assistance processing signal. The hearing assistance processing
unit 10 performs processing for providing directivity described above and
amplifies the signal matched with the hearing characteristic, etc., but
these processes are similar to the processing of the related-art hearing
aid and therefore will not be described again in detail.

[0026] As shown in FIG. 3, the microphone sensitivity correction value
calculation unit 11 includes: a digital filter 17a (first digital filter)
connected on an output side of the A/D converter 8a; a digital filter 17b
(second digital filter) connected on an output side of the A/D converter
8b; a correction unit 18 connected on an output side of the digital
filter 17b; a comparison unit 19 to which an output signal of the
correction unit 18 and an output signal of the digital filter 17a are
input; and a correction value update unit 20 connected on an output side
of the comparison unit 19. The microphone sensitivity correction value
calculation unit 11 further includes: a memory 21 connected on an output
side of the correction value update unit 20; and a selector 22 to which
an output signal of the memory 21 and an output signal of the correction
value update unit 20 are input, and which is configured to select and
output one of the signals input thereto.

[0027] Each of the digital filter 17a and the digital filter 17b includes
a plurality of FIR (Finite Impulse Response) filters. One function is to
smooth the amplitude of a digital input signal. Thus, a moving average of
amplitude values continuous in time series of digital input signal is
computed. Another function is to shut off high frequency to execute
microphone sensitivity correction using a signal in a low frequency area
where amplitude fluctuation of digital input signal is small.

[0028] The correction unit 18 corrects the amplitude value of an output
signal of the digital filter 17b using the correction value output by the
correction value update unit 20. Since the configuration is the same as
that of the microphone sensitivity correction unit 9 described above, and
the configuration is not be described again in detail.

[0029] The comparison unit 19 compares the amplitude value of the output
signal of the digital filter 17a and the amplitude value of the output
signal of the correction unit 18 and outputs the comparison result to the
correction value update unit 20. The comparison is made every one clock
of the operation clock. The comparison result indicates three states.
Here, the comparison unit 19 outputs "2" if the amplitude value of the
output signal of the digital filter 17a is larger; the comparison unit 19
outputs "1" if the amplitude value of the output signal of the correction
unit 18 is larger; and the comparison unit 19 outputs "0" if both are the
same.

[0030] The correction value update unit 20 generates the microphone
sensitivity correction value to correct the amplitude of the input signal
in the microphone sensitivity correction unit 9 and the correction unit
18 based on the input signal from the comparison unit 19. The microphone
sensitivity correction value is a coefficient to be multiplied by the
amplitude of a signal to make a correction. When the amplitude is not
corrected, namely, the outputs of the front microphone and the rear
microphone are the same, the microphone sensitivity correction value
becomes 1.0. When the amplitude of the output signal of the front
microphone is larger than the amplitude of the output signal of the rear
microphone, the microphone sensitivity correction value becomes a numeric
value exceeding 1 such as 1.1 to increase the amplitude of the output
signal of the rear microphone. On the other hand, the amplitude of the
output signal of the front microphone is smaller than the amplitude of
the output signal of the rear microphone, the microphone sensitivity
correction value becomes a numeric value smaller than 1 such as 0.9 to
decrease the amplitude of the output signal of the rear microphone.

[0031] The microphone sensitivity correction value is updated as described
below. First, a memory (not shown) is provided in the correction value
update unit 20, and an initial value, an increment value, and a decrement
value are stored in the memory. For example, the initial value is set to
1.0000 and the increment value and the decrement value are set to 0.0001.
When the operation of the microphone sensitivity correction value
calculation unit 11 is started, the initial value is set to the
microphone sensitivity correction value. Then, every one clock of the
operation clock, when the signal input from the comparison unit 19 is 2,
the increment value is added to the microphone sensitivity correction
value, and when the signal input from the comparison unit 19 is 1, the
decrement value is subtracted from the microphone sensitivity correction
value, and the result value is output as a new microphone sensitivity
correction value. For example, when the microphone sensitivity correction
value one operation clock before is 1.0001, if 1 is input from the
comparison unit 19, the microphone sensitivity correction value output
from the correction value update unit 20 at the current clock becomes
1.0001. If the microphone sensitivity difference is previously known and
an appropriate microphone sensitivity correction value can be calculated,
an appropriate value for correcting the sensitivity difference may be
previously adopted as the initial value rather than 1.0001. The increment
value and the decrement value may be different values.

[0032] The microphone sensitivity correction value output by the
correction value update unit 20 is output to the storage unit 12 and the
failure detection unit 13 and is also output to the memory 21 and the
selector 22 provided in the microphone sensitivity correction value
calculation unit 11. An output signal of the selector 22 is transmitted
to the microphone sensitivity correction unit 9 as the microphone
sensitivity correction value and the digital input signal output by the
A/D converter 8b is multiplied by the value.

[0033] The operation of the memory 21 and the selector 22, namely, a
determination method of the microphone sensitivity correction value for
making a sensitivity correction will be described. A control signal (not
shown in FIG. 3) is input to the memory 21 and the selector 22 from the
control unit 16. The memory 21 performs the storage operation of the
microphone sensitivity correction value output by the correction value
update unit 20 and the output operation to the selector 22 in accordance
with the control signal. The selector 22 selects one of the microphone
sensitivity correction value output by the correction value update unit
20 and the output signal of the memory 21 in accordance with the control
signal and outputs the selected value or signal to the microphone
sensitivity correction unit 9 as the microphone sensitivity correction
value.

[0035] On the other hand, if the sensitivity correction is performed by
fixedly using the microphone sensitivity correction value updated at a
specific time, the selector 22 selects and outputs the output value of
the memory 21. The specific time refers to the initial adjustment time at
the factory shipment time, the time of the stationary state after a
battery is inserted into the battery insertion port 6 and power of the
hearing aid is turned on, or the user-specified time. Thus, the memory 21
stores the microphone sensitivity correction value output by the
correction value update unit 20 at the time (clock) instructed by the
control unit 16 and stores the value until a next command is received
from the control unit 16. The memory continues to output the stored value
to the selector 22. Further, the selector 22 selects the output value of
the memory 21 and output the value as the microphone sensitivity
correction value. Accordingly, the microphone sensitivity correction unit
9 performs sensitivity correction by using the microphone sensitivity
correction value at the specific time as a fixed value.

[0036] In the hearing aid of this embodiment, two sensitivity correction
determination methods described above are set as function modes of the
hearing aid, and one of the two function modes is selected for use by
switching the selector 22. If only one of the function modes is
implemented as the function of the hearing aid, only the selector 22 may
be removed or both the memory 21 and the selector 22 may be removed from
the configuration shown in FIG. 3.

[0037] Referring again to FIG. 2, the storage unit 12 will be described.
The storage unit 12 stores the output signal of the hearing assistance
processing unit 10 and the output signal of the microphone sensitivity
correction value calculation unit 11 in separate storage areas. The
signal output from the hearing assistance processing unit 10 is, for
example, a gain selected when the hearing assistance processing unit 10
performs hearing assistance processing or the like and is mainly an
operation history of the hearing assistance processing unit 10. The
operation history stored in the storage unit 12 is transferred to a
device outside the hearing aid, such as a fitting device using an
input/output interface (not shown). This operation is the same as that of
the related hearing aid and therefore will not be described again in
detail.

[0038] The output signal of the microphone sensitivity correction value
calculation unit 11 input to the storage unit 12 is the microphone
sensitivity correction value output by the correction value update unit
20 shown in FIG. 3. The storage unit 12 has a plurality of storage areas
for storing the microphone sensitivity correction value and is configured
to store the value in accordance with a control signal of the control
unit 16 and output the stored microphone sensitivity correction value to
the failure detection unit 13 in accordance with a control signal of the
control unit 16.

[0039] Similar to the operation history, the microphone sensitivity
correction value stored in the storage unit 12 is also transferred to a
device outside the hearing aid, such as a fitting device using the
input/output interface (not shown). Thus, the stored microphone
sensitivity correction value can be read by a device such as the fitting
device, and the past microphone state can be analyzed.

[0040] The timing at which the storage unit 12 stores the microphone
sensitivity correction value will be described. The storage unit 12
stores the microphone sensitivity correction value first calculated when
the hearing aid of the embodiment is manufactured. The first calculated
microphone sensitivity correction value is the most recent value of the
microphone sensitivity correction value updated at one specific time
described above. If the hearing aid is set such that the microphone
sensitivity correction unit 9 performs the sensitivity correction by
using the microphone sensitivity correction value always updated during
the operation of the hearing aid, the storage unit 12 stores the
microphone sensitivity correction value after a predetermined time has
elapsed since the start of using the hearing aid.

[0041] Second or subsequent storage of the microphone sensitivity
correction value is executed, for example, every month, because the
amplitudes of the output signals of the microphone 3a and the microphone
3b may vary due to aging. Change per time by the aging is very small as
compared with amplitude decrease of the output signal at the failure of
the microphone, which is to be solved by the application.

[0042] The storage unit 12 stores the first stored microphone sensitivity
correction value and the second and subsequent stored microphone
sensitivity correction values in separate storage areas. The first stored
microphone sensitivity correction value is held without being overwritten
with another value. The second or subsequent stored microphone
sensitivity correction value may be overwritten every time or may be
stored in a separate area every time together with the storage order
information without being overwritten. The storage unit 12 outputs the
first stored microphone sensitivity correction value and the second and
subsequent stored microphone sensitivity correction values to the failure
detection unit 13.

[0043] As shown in FIG. 4, the failure detection unit 13 includes an
abnormal value setting unit 23 connected on an output side of the storage
unit 12, an abnormal value detection unit 24 to which an output signal of
the abnormal value setting unit 23 and an output signal of the microphone
sensitivity correction value calculation unit 11 are input, and an
abnormal time detection unit 25 connected on an output side of the
abnormal value detection unit 24.

[0044] The abnormal value setting unit 23 calculates a threshold value
whether the microphone sensitivity correction value is an abnormal value
by using an output signal of the storage unit 12, and outputs the
threshold value to the abnormal value detection unit 24. First, the
abnormal value setting unit 23 calculates a center value to set the
threshold value from the signal input from the storage unit 12 as
described below.

[0045] First, when the storage unit 12 has only the first stored
microphone sensitivity correction value, namely, when the second or
subsequent microphone sensitivity correction value is not yet stored, the
first stored microphone sensitivity correction value is adopted as the
center value.

[0046] On the other hand, when the storage unit 12 has the second or
subsequent stored microphone sensitivity correction value, the second or
subsequent stored microphone sensitivity correction value is used as
candidates for the center value. If the storage unit 12 has a plurality
of second and subsequent stored microphone sensitivity correction values,
the most recent value or an average value of a plurality of values from
the most recent value is used as the candidate for the center value.
Thereafter, the candidate for the center value is compared with the first
stored microphone sensitivity correction value. When the candidate for
the center value is in the range of 0.7 times to 1.5 times the first
stored microphone sensitivity correction value, the candidate for the
center value is adopted as the center value; and when the candidate is
not in the range, the first stored microphone sensitivity correction
value is adopted as the center value.

[0047] The reason why the second or later microphone sensitivity
correction value stored in the storage unit 12 is used as the candidate
for the center value is because whether the microphone fails is
determined based on performance of the microphone at the time point of
failure detection considering the effect of aging. The purpose of
comparing the candidate for the center value with the first stored
microphone sensitivity correction value is to detect a failure even if
the effect is caused by aging, when the microphone sensitivity correction
value shifts in a predetermined range or more, that is, when the output
difference between the front microphone and the rear microphone becomes
larger than a predetermined range.

[0048] When the center value is thus determined, then the abnormal value
setting unit 23 sets a threshold value TH_H and a threshold value TH_L.
The threshold value TH_H is a threshold value on a higher side of the
microphone sensitivity correction value, and the threshold value TH_L is
a threshold value on a lower side of the microphone sensitivity
correction value. The abnormal value setting unit 23 includes a memory
(not shown) and stores an increment value and a decrement value in the
memory. The threshold value TH_H is set as a value obtained by adding the
increment value to the center value. The threshold value TH_L is set as a
value obtained by subtracting the decrement value from the center value.
The threshold value TH_H and the threshold value TH_L are output to the
abnormal value detection unit 24. For example, when the increment value
is 0.5000 and the decrement value is 0.3000, and when the center value is
1.0021, the threshold value TH_H becomes 1.5021 and the threshold value
TH_L becomes 0.7021.

[0049] Next, the abnormal value detection unit 24 will be described. The
microphone sensitivity correction value output by the microphone
sensitivity correction value calculation unit 11, the threshold value
TH_H and the threshold value TH_L output by the abnormal value setting
unit 23, and the control signal output by the control unit 16 are input
to the abnormal value detection unit 24. The abnormal value detection
unit 24 outputs an abnormal value detection signal to the abnormal time
detection unit 25 as the result of comparing the microphone sensitivity
correction value and the threshold value TH_H and the threshold value
TH_L. This comparison is made every clock of the operation clock. When
the microphone sensitivity correction value is equal to or more than the
threshold value TH_H or when the microphone sensitivity correction value
is equal to or less than the threshold value TH_L, the abnormal value
detection signal becomes 1; otherwise, the abnormal value detection
signal becomes 0. If the control signal from the control unit 16
validates the comparison result, namely, control is performed so as not
to execute failure detection in the failure detection unit 13, the
abnormal value detection signal becomes 0 regardless of the microphone
sensitivity correction value.

[0050] The operation of the abnormal value detection unit 24 will be
described with reference to FIGS. 5A and 5B. FIGS. 5A and 5B show
schematically an example of a time change in the microphone sensitivity
correction value. In FIG. 5A, a failure occurs in the front microphone at
time Ta1 and the amplitude of an output signal of the microphone 3a
becomes small, and thus the microphone sensitivity correction value
becomes gradually small so as to bring the amplitude of the output signal
of the rear microphone close to that of the front microphone. At time
Ta2, the microphone sensitivity correction value falls below the
threshold value TH_L. At time Ta3, the amplitude value of the output
signal of the digital filter 17a and the amplitude value of the output
signal of the correction unit 18 become the same and the microphone
sensitivity correction value is a constant value. At this case, the
abnormal value detection signal becomes 0 from time T0 to Ta2 and becomes
1 after Ta2.

[0051] On the other hand, in FIG. 5B, a failure occurs in the rear
microphone at time Tb1 and the amplitude of an output signal of the
microphone 3b becomes small and thus the microphone sensitivity
correction value becomes gradually large so as to bring the amplitude of
the output signal of the rear microphone close to that of the front
microphone. At time Tb2, the microphone sensitivity correction value
exceeds the threshold value TH_H. At time Tb3, the amplitude value of the
output signal of the digital filter 17a and the amplitude value of the
output signal of the correction unit 18 become the same and the
microphone sensitivity correction value is a constant value. At this
case, the abnormal value detection signal becomes 0 from time T0 to Tb2
and becomes 1 after Tb2.

[0052] Next, the abnormal time detection unit 25 will be described. The
abnormal value detection signal output by the abnormal value detection
unit 24 is input to the abnormal time detection unit 25, and the abnormal
time detection unit 25 determines whether a failure occurs in the
microphone based on the abnormal value detection signal and outputs a
failure detection signal to the sound output unit 14.

[0053] Thus, the abnormal time detection unit 25 includes a counter (not
shown) for counting from 0 to the maximum count (C_max). When the
abnormal value detection signal is 1, the counter is incremented by one;
and when the abnormal value detection signal is 0, the counter is
decremented by one. In a case where the abnormal value detection signal 0
is input when the value of the counter is 0, the value of the counter
maintains 0. In a case where the abnormal value 1 is input when the value
of the counter is C_max, the value of the counter maintains C_max.

[0054] When the value of the counter is equal to or more than a counter
threshold value C_th set in the abnormal time detection unit 25, the
abnormal time detection unit 25 determines that a failure occurs in the
microphone 3a or the microphone 3b, and sets a failure detection signal
to 1. On the other hand, when the value of the counter is smaller than
the counter threshold value C_th, the abnormal time detection unit 25
determines that a failure does not occur in the microphone 3a or the
microphone 3b, and sets the failure detection signal to 0 and outputs the
signal to the sound output unit 14. The operation of the abnormal time
detection unit 25 is executed every one clock of the operation clock.

[0055] As described above, when the failure detection unit 13 detects that
a given time period has elapsed in a state in which the microphone
sensitivity correction value output by the microphone sensitivity
correction value calculation unit 11 becomes outside a specified range,
the failure detection unit 13 determines that a failure occurs in the
microphone.

[0056] Referring again to FIG. 2, the sound output unit 14 will be
described. The sound output unit 14 receives a digital hearing assistance
processing signal subjected to hearing assistance processing and output
by the hearing assistance processing unit 10 and the failure detection
signal output by the failure detection unit 13, determines a sound
provided for the user as the hearing aid, and outputs the sound to the
D/A converter 15.

[0057] As shown in FIG. 6, the sound output unit 14 includes: an alarm
sound generation unit 26 connected to the output of the failure detection
unit 13; and an output sound selection unit 27 to which an output signal
of the alarm sound generation unit 26 and an output signal of the hearing
assistance processing unit 10 are input, and which is configured to
select one of the output signal of the alarm sound generation unit 26 and
the output signal of the hearing assistance processing unit 10 and to
output the selected signal to the D/A converter 15.

[0058] The alarm sound generation unit 26 generates an alarm sound based
on the failure detection signal output by the failure detection unit 13.
More particularly, while the failure detection signal is 1, the alarm
sound generation unit 26 generates an alarm sound and outputs it to the
output sound selection unit 27; while the failure detection signal is 0,
the alarm sound generation unit 26 does not generate an alarm sound. The
alarm sound is a monotonous continuous sound such as a beep sound, and
the sound volume and the frequency are matched with the hearing
characteristic of the user used as the reference when the hearing
assistance processing unit 10 performs hearing assistance processing and
are set to the level at which the user hears most comfortable. The alarm
sound may be music or a voice.

[0059] The output signal of the hearing assistance processing unit 10 and
the output signal of the alarm sound generation unit 26 are input to the
output sound selection unit 27. Based on the failure detection signal
output by the failure detection unit 13, when the failure detection
signal is 0, the output sound selection unit 27 selects the output signal
of the hearing assistance processing unit 10; and when the failure
detection signal is 1, the output sound selection unit 27 selects the
output signal of the alarm sound generation unit 26 and outputs the
selected signal to the D/A converter 15. That is, when the failure
detection unit 13 determines that a failure does not occur in the
microphone 3a or the microphone 3b, a sound subjected to hearing
assistance processing is output; otherwise, an alarm sound is output.

[0060] The D/A converter 15 converts the digital signal output by the
sound output unit 14 into an analog signal and outputs the analog signal
to the receiver 7. This operation is performed by using the same
operation clock as the A/D converter 8a and the A/D converter 8b.

[0061] The receiver 7 is a speaker for converting the analog signal output
by the D/A converter 15 into an acoustic signal and outputting the
acoustic signal.

[0062] The control unit 16 generates various control signals for
controlling the microphone sensitivity correction value calculation unit
11, the storage unit 12, and the failure detection unit 13. The control
unit 16 includes a memory storing an operation program of the hearing aid
and a CPU (Central Processing Unit) for executing the program, and
executes the program so as to generate various control signals at the
timings described above. The control unit 16 controls the whole hearing
aid including the function components shown in FIG. 2, but the operation
for controlling other than the function components of the feature of the
embodiment will not be described.

[0063] Next, an operation example of failure detection of the feature of
the embodiment will be described with reference to FIGS. 7A to 7C. FIG.
7A shows the microphone sensitivity correction value output by the
microphone sensitivity correction value calculation unit 11, FIG. 7B
shows the value of the counter in the abnormal time detection unit 25 in
the failure detection unit 13, and FIG. 7D shows the failure detection
signal output by the failure detection unit 13. FIGS. 7A to 7C show the
case where the front microphone (microphone 3a) fails at time Tc, and the
amplitude of the output signal of the microphone 3a becomes drastically
small.

[0064] When the amplitude of the output signal of the microphone 3a
becomes small at the time Tc, the microphone sensitivity correction value
starts to decrease such that the amplitude of the output signal of the
rear microphone (microphone 3b) becomes the same as the amplitude of the
output signal of the microphone 3a. When the microphone sensitivity
correction value becomes equal to or less than the threshold value TH_L
at time Td, the value of the counter starts to increase. Thereafter, the
decrease in the microphone sensitivity correction value stops. However,
since the microphone sensitivity correction value is smaller than the
threshold value TH_L, the value of the counter continues to increase
(from time Td to time Te).

[0065] When the value of the counter becomes equal to or more than the
counter threshold value C_th at time Te, the failure detection signal
changes from 0 to 1. At this time, output of an alarm sound is started
from the receiver 7 and thus the user can recognize that one of the front
microphone and the rear microphone fails. At this point in time, however,
the user cannot determine which microphone fails. Then, the value of the
counter still increases, and when the value reaches the maximum count
C_max, the counter continues to hold the value.

[0066] Time Tg represents the time at which the user closes the rear
microphone (microphone 3b) with a finger. At this time, while the
amplitude of the output signal of the microphone 3a remains small, the
amplitude of the output signal of the microphone 3b becomes small.
Therefore, the microphone sensitivity correction value starts to
increase. When the microphone sensitivity correction value becomes larger
than the threshold value TH_L at time Th, the value of the counter starts
to decrease from the maximum count value C_max.

[0067] When the value of the counter becomes smaller than the counter
threshold value C_th at time Ti, the failure detection signal changes
from 1 to 0. Then, the alarm sound output from the receiver 7 stops, and
a sound subjected to hearing assistance processing is again output.

[0068] Time Tj is the time at which the user releases the finger which has
closed the rear microphone. The amplitude of the output signal of the
microphone 3b becomes large, and a difference from the amplitude of the
output signal of the microphone 3a occurs. Consequently, the microphone
sensitivity correction value again starts to decrease. At this time, the
value of the counter still continues to decrease. At time Tk, the
microphone sensitivity correction value becomes equal to or less than the
threshold value TH_L, and change of the value of the counter transits
from decrease to increase. At time TL, the value of the counter again
becomes equal to or more than the counter threshold value T_th, and the
sound output from the receiver 7 changes to an alarm sound.

[0069] Accordingly, the user can easily know that the microphone (rear
microphone) closed with a finger normally operates, and the other
microphone (front microphone) fails. On the other hand, if the front
microphone fails as in the example described above, beeping of an alarm
sound does not stop for a while after the user closes the front
microphone with a finger at time Tg. At this time, the user can recognize
that the microphone not closed with a finger (rear microphone) normally
operates, and the user can estimate that the microphone closed with the
finger (front microphone) fails.

[0070] If the rear microphone fails, similarity applies. That is, when the
front microphone is closed with a finger, an alarm sound and a sound
subjected to hearing assistance processing are switched and output in
association with the operation, and the user can easily know that the
microphone closed with the finger (front microphone) normally operates
and the other microphone (rear microphone) fails.

[0071] The embodiment describes the example in which the user can
recognize which of the two microphones fails by operation of the user.
However, the receiver 7 may output an alarm sound so as to indicate which
microphone fails.

[0072]FIG. 8 shows the configuration of the failure detection unit 13 for
outputting the alarm sound. This configuration differs from the
above-described configuration in that the abnormal time detection unit 25
includes a front microphone counter 25a (first counter) and a rear
microphone counter 25b (second counter).

[0073] Further, the specification of the abnormal value detection signal
output by the abnormal value detection unit 24 is changed. More
particularly, when the microphone sensitivity correction value output by
the microphone sensitivity correction value calculation unit 11 becomes
equal to or more than the threshold value TH_H, the abnormal value
detection signal indicates 2; when the microphone sensitivity correction
value becomes equal to or less than the threshold value TH_L, the
abnormal value detection signal indicates 1; and when the microphone
sensitivity correction value is larger than the threshold value TH_L and
is smaller than the threshold value TH_H, the abnormal value detection
signal indicates 0.

[0074] When the abnormal value detection signal is 2, the abnormal time
detection unit 25 increments the rear microphone counter 25b by one and
decrements the front microphone counter 25a by one. When the abnormal
value detection signal is 1, the abnormal time detection unit 25
increments the front microphone counter 25a by one and decrements the
rear microphone counter 25b by one. Further, when the abnormal value
detection signal is 0, the abnormal time detection unit 25 decrements
both the front microphone counter 25a and the rear microphone counter 25b
by one.

[0075] The specification of the failure detection signal output by the
abnormal time detection unit 25 is also changed. More particularly, when
the value of the rear microphone counter 25b becomes equal to or more
than the counter threshold value C_th, the failure detection signal
becomes 2; when the value of the front microphone counter 25a becomes
equal to or more than the counter threshold value C_th, the failure
detection signal becomes 1; and when both the value of the front
microphone counter 25a and the value of the rear microphone counter 25b
become smaller than the counter threshold value C_th, the failure
detection signal becomes 0. That is, when the failure detection signal is
2, the rear microphone (microphone 3b) fails; when the failure detection
signal is 1, the front microphone (microphone 3a) fails; and when the
failure detection signal is 0, neither of the microphones fails.

[0076] Further, the operation of the sound output unit 14 is also changed.
First, in the alarm sound generation unit 26, when the failure detection
signal is 2, a continuous sound of a beep sound is generated. When the
failure detection signal is 1, a sound such that a short sound of a beep
sound is repeated at given intervals is generated. When the failure
detection signal is 0, an alarm sound is not generated.

[0077] Next, when the failure detection signal is 2 or 1, the output sound
selection unit 27 selects and outputs an alarm sound output by the alarm
sound generation unit 26, and when the failure detection signal is 0, the
output sound selection unit 27 selects and outputs an output signal of
the hearing assistance processing unit 10.

[0078] Therefore, when the front microphone fails, an alarm sound of a
short repetitive sound is output, and when the rear microphone fails, an
alarm sound of a continuous sound is output. This means that the length
of the output alarm sound is changed in response to the failing
microphone. Accordingly, the user can easily know which of the two
microphones fails.

[0079] The alarm sound generated by the alarm sound generation unit 26 may
be music or a voice informing the user which microphone fails. At this
time, the type of alarm sound, the type of music, the type of voice,
etc., is changed in response to which microphone fails.

[0080] The embodiment discloses the example in which when the microphone
fails, only an alarm sound is output from the receiver 7. However, an
alarm sound may be combined with the sound subjected to hearing
assistance processing by the hearing assistance processing unit 10, and
the synthesized sound may be output.

[0081] Thus, the sound output unit 14 is provided with an output sound
synthesis unit in place of the output sound selection unit 27. When the
failure detection signal output by the failure detection unit 13
indicates a failure of the microphone, the output sound synthesis unit
combines the alarm sound output by the alarm sound generation unit 26
with the output signal of the hearing assistance processing unit 10, and
outputs the result to the D/A converter 15.

[0082] With this configuration, the user can recognize a failure of the
microphone while hearing the surrounding sound, and can continue to use
the hearing aid until the failure of the microphone is repaired.

[0083] As described above, the hearing aid in the embodiment includes: the
first microphone; the first A/D converter connected on the output side of
the first microphone; the second microphone; the second A/D converter
connected on the output side of the second microphone; the microphone
sensitivity correction unit connected on the output side of the second
A/D converter; the hearing assistance processing unit to which the output
of the microphone sensitivity correction unit and the output of the first
A/D converter are input; the microphone sensitivity correction value
calculation unit to which the output of the first A/D converter and the
output of the second A/D converter are input, and one output of which is
connected to the microphone sensitivity correction unit; the storage unit
connected to another output of the microphone sensitivity correction
value calculation unit; the failure detection unit to which the output of
the storage unit and a signal output from the another output of the
microphone sensitivity correction value calculation unit are input; the
sound output unit to which an output signal of the failure detection unit
and an output signal of the hearing assistance processing unit are input;
the D/A converter connected on the output side of the sound output unit;
and the receiver connected on the output side of the D/A converter.
Accordingly, the user can recognize a failure of the microphone.

[0084] Further, according to the embodiment, when one microphone fails,
the user can easily recognize which of the microphones fails by simple
operation of the user or without operation of the user.

[0085] According to the embodiment, the microphone sensitivity correction
value is stored in the storage unit 12, whereby it is possible to later
determine when an anomaly has occurred by reading the storage unit 12.

[0086] In the embodiment, the failure detection unit 13 includes the
abnormal time detection unit 25, but the abnormal time detection unit 25
may be eliminated. At the time, the abnormal value detection signal
output by the abnormal value detection unit 24 is adopted as an output
signal from the failure detection unit 13 to the sound output unit 14.

[0087] In the embodiment, the in-the-ear hearing aid is illustrated in
FIG. 1, but a hearing aid of any other type such as a behind-the-ear
hearing aid or an pocket hearing aid may be applied so long as the
hearing aid uses two microphones.

[0088] While the invention has been described in detail with reference to
the specific embodiments, it is apparent to those skilled in the art that
various changes and modifications may be made without departing from the
spirit and the scope of the invention.

[0089] This application is based on Japanese Patent Application No.
2009-025743 filed on Feb. 6, 2009, contents of which are incorporated
herein by reference.

[0090] According to the embodiment, the user can recognize a failure of
the microphone. Further, the microphone sensitivity correction value is
stored, whereby it is possible to determine when an anomaly has occurred
by reading the storage unit. When a failure of the microphone is detected
by using the microphone sensitivity correction value, sound indicating
the failure of the microphone is generated, whereby the user can
recognize the failure of the microphone by hearing the sound.

[0091] The hearing aid according to the embodiment can make the user
recognize failure of the microphone and can be widely applied to hearing
aid devices.